Underwater welding has numerous important applications in a broad range of industries, such as fabrication and repair of marine structures, pipelines, vessels, and nuclear and petrochemical facilities. The procedure can be performed in either a "dry" mode where water near the weld site is evacuated using a hyperbaric chamber, or in a "wet" mode where water is allowed to contact the weld site. While in-air quality welds can be obtained using the "dry" mode, the hyperbaric chamber is expensive and is difficult to maneuver and handle.
Typically, wet welding techniques include shielded metal arc welding, gas metal arc welding, flux cored arc welding, friction welding, explosive welding and stud welding. Other techniques include water and gas shielded gas tungsten arc welding, friction stitch welding, use of flexible, reduced stress weld connections, welding within rotating, pressure reducing pipes and chambers, and welding within partially open, work piece-attached chambers.
Although many wet welding techniques have been developed, significant metallurgical, mechanical and operational problems remain. In particular, relative to in-air or dry mode welds, wet welds tend to exhibit high porosity, increased hydrogen embrittlement, increased solidification cracking, reduced weld strength, and reduced weld toughness. These problems are caused by rapid cooling and entrapment of steam and hydrogen within the weld. Underwater welding typically produces hydrogen by the decomposition of water between the arc and the work piece. Rapid cooling of the weld material traps the hydrogen inside the weld. As a result, the weld is porous and embrittled by hydrogen. Moreover, during welding the work piece becomes hot, causing steam and rising hydrogen bubbles to create a region of oscillating pressure around the arc.
In addition, the rapid formation of dark, water-borne particulate plumes near the weld site poses a significant operational problem. The plumes may impair and even prevent visual inspection and monitoring of the weld.
In view of the foregoing, it would be highly desirable to provide an improved technique for underwater welding. The technique should provide an underwater weld with reduced porosity and increased solidification. In addition, the technique should work with existing welding techniques.